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Mechanoacoustic and microscopic study of aluminous porcelain resistance to structural degradation

Ranachowski P., Rejmund F., Ranachowski Z., Pawełek A., Piątkowski A., Kudela S.

Archives of Metallurgy and Materials

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2011

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Vol. 56, iss. 4

1127-1233

EN

The paper presents mechanoacoustic and microscopic testing of degradation processes of modern C 120 electrotechnical porcelain of domestic medium voltage line insulator. Samples of small dimensions, cut off from the rod of insulator, were subjected to compressive loading, with recording of acoustic emission descriptors. Microscopic analysis enabled determining the advancement of degradation effects. Three stages of the structure degradation were distinguished. The effectiveness of dispersive and fibrous reinforcement of modern aluminous porcelain C 120 type has been described. Structural strengthening by corundum grains and mullite needle shaped crystals improves mechanical parameters and distinguishes this material from typical aluminosilicate ceramics. The presented results enable drawing up the conclusions concerning the resistance of investigated material to the ageing degradation process development during long term operation.

PL

W pracy przedstawiono mechanoakustyczne i mikroskopowe badania procesów degradacji w nowoczesnym tworzywie porcelanowym rodzaju C 120 liniowego izolatora SN. Małogabarytowe próbki, wycięte z pnia izolatora, były quasi-statycznie ściskane z jednoczesną rejestracją deskryptorów emisji akustycznej. Badania mikroskopowe ściskanych próbek wykorzystano do opisu mechanizmu degradacji tworzywa. Wyróżniono trzy kolejne etapy degradacji struktury tworzywa. Stwierdzono wysoką krótko- i długotrwałą odporność materiału izolatora w porównaniu do typowych tworzyw rodzaju C 120. Jest to wynikiem skutecznego dyspersyjnego i włóknistego wzmocnienia struktury czerepu badanej porcelany

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Aluminous porcelain degradation study using mechanoacoustic and microscopic methods

Ranachowski P., Rejmund F., Ranachowski Z., Pawełek A., Piątkowski A.

Archives of Electrical Engineering

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2011

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Vol. 60, nr 2

109-128

EN

This experimental paper comprises the results of acoustic emission (AE), microscopic and ultrasonic measurements of samples subjected to slowly increasing compressive stress. On the basis of conducted measurements the successive stages of the material structural degradation have been recognized. The objects of study were samples made of C 120 aluminous porcelain. The investigated material has found at present the application in the fabrication of technical elements like overhead power line insulators. In the case of such objects, not only high mechanical strength, but especially elevated durability as well as operational reliability are required. The expected "life time" of net insulators during exploitation is about 40 years. The analysis of obtained mechanoacoustic dependences pointed out a complex mechanism of degradation of the material. Microscopic investigation of samples, which were stressed to different levels of load, enabled to specify the development of gradual growth of microcracks and successive crushing out of elements of the structure. These processes appear to be similar to the ageing processes occurring in the material during long period of exploitation under a working load. Three stages of the structure degradation were distinguished. The preliminary and subcritical ones show low or moderate intensity of AE signals and considerable variety for the particular samples. The critical stage directly precedes the destructtion of samples. Its range is relatively narrow and reveals the AE activity of high energy. The effectiveness of dispersive and fibrous reinforcement of modern aluminous porcelain C 120 type has been described. Structural strengthening by corundum grains and mullite needle shaped crystals improves mechanical parameters and distinguishes this material from typical aluminosilicate ceramics. The presented results enable drawing up the conclusions concerning the resistance of investigated material to the ageing degradation process development during long term operation.

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Comparison of Acoustic Emission and Structure Degradation in Compressed Porcelain and Corundum Materials

Ranachowski P., Rejmund F., Ranachowski Z., Pawełek A., Piątkowski A.

Archives of Acoustics

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2009

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Vol. 34, No. 4

655-676

EN

The paper presents the results of acoustic emission (AE), microscopic and ultrasonic measurements of the samples subjected to slowly increasing compressive stress. On the basis of performed measurements, the successive stages of the materials structural degradation have been recognized. The object of research and comparison were the samples made of the electrotechnical materials – aluminous porcelain and corundum ceramics. Both investigated materials have wide technical application. The analysis of obtained mechanoacoustic characteristics pointed out a complicated mechanism of degradation of the materials. Microscopic investigation of samples, which were stressed to different levels of load, enabled to specify the various course of the gradual growth of microcracks and successive crushing out of elements of the structure. These effects appear to be similar to the aging processes occurring in the materials during long periods of exploitation under working load. For the two tested materials there were distinguished three stages of the structure degradation. The preliminary and subcritical ones show low or moderate intensity of AE signals and considerable variety for the particular samples. The critical stage directly precedes destruction of the samples. Its range is relatively narrow and contains AE activity of high energy. The presented results enable to draw up conclusions concerning the resistance of investigated materials to the aging degradation processes development during long-term operation. Comparison of the results of mechanical, acoustic and microscopic studies have revealed that the differences registered for the strength and characteristics are due to inhomogeneities of the materials in the semi-macro as well as in the micro-scale. The effectiveness of dispersive and fibrous reinforcement of aluminous porcelain was described. Strengthening of porcelain by corundum grains and mullite needleshaped crystals improves mechanical parameters and distinguishes this material from typical aluminosilicate ceramics. The occurrence of groupings of bigger grains in the structure of the corundum material represents most probably the intermediate state, leading to the known effect of the abnormal grain growth (AGG).